PubMed Health⌕ Search

Biomedical subjects

J Catalán

Publications and source records attributed to J Catalán.

At least 19 recordsLinked to original sources
PubMed2006

On the photophysics of all-trans polyenes: hexatriene versus octatetraene.

The disparate photophysical behavior of trans-1,3,5-hexatriene (nonfluorescent) and trans-1,3,5,7-octatetraene (with two fluorescence emissions) in the gas phase is explained in terms of the tendency of their 1B(u) excited states to rotate about their terminal carbon-carbon single bonds in order to adopt a quasiplanar molecular form of lower energy than the 1B(u) state in the parent all-trans structure. The origin of their disparate photophysical behavior is that such a transformation is subject to a small energy barrier in octatetraene; the barrier produces two minima (two fluorescence emissions) in the corresponding potential-energy curve. Instead of an energy barrier, hexatriene gives a 1,3-diene species which falls to the ground state so rapidly that no emission is produced.

Journal Article↗
PubMed2005

The molecular symmetry and electronic spectroscopy of 7-azaindole dimer: its proton-transfer channels.

The potential-energy surfaces for the proton transfer in the doubly hydrogen-bonded dimer of 7-azaindole in its lowest excited electronic states were examined. The dimer with C2h symmetry in its lowest excited electronic states, 2Ag and 1Bu, undergoes concerted double-proton transfer via transition states of the same symmetry placed at energies 4.55 and 4.70 kcal/mol higher, respectively. This suggests that the activation barriers for the double-proton transfer, if any, are lower than 1 kcal/mol. Emission from the dimers resulting from the double-proton transfer involves a Stokes shift of 5605 cm(-1), as theoretically estimated from the 0-0 components of the absortion and emission transitions of the dimer. Surprisingly, however, the calculations suggest that the green emission cannot arise from the 2Ag state generated by a double-proton transfer, because this structure possesses an imaginary frequency. In the 7-azaindole dimer of Cs symmetry, the first excited electronic state, a', lies 4.9 kcal/mol below 1Bu. This excited state a' can be the starting point for single-proton transfers giving a zwitterionic form that can dissociate into the protonated and deprotonated forms of 7-azaindole, the former being electronically excited. This situation of lower symmetry is consistent with the mutational scheme proposed by Goodman [Nature (London) 378, 237 (1995)].

Journal Article↗
PubMed2005

Study of 7-azaindole in its first four singlet states.

The molecular structure and properties of 7-azaindole in its first four singlet states were studied with a view to improving current understanding of the photophysical behavior of its C(2h) dimer. This dimer, which exhibits a double proton transfer via its two hydrogen bonds upon electronic excitation, has for 35 years been used as a model for the photophysical behavior of DNA base pairs. Electronic excitation of 7-azaindole simultaneously increases its acidity and basicity; these changes facilitate a concerted mechanism for the double proton transfer in the dimer. In this work, we found the acidity and basicity changes to occur only in its first pi,pi(*) excited singlet state.

Journal Article↗
PubMed2004

On the ordering of the first two excited electronic states in all-trans linear polyenes.

Reported experimental evidence of the relative position of the first two excited electronic states in linear polyenes was carefully examined and compared with that derived from time dependent density functional theory (TDDFT) theoretical calculations performed at the B3LYP level on optimized geometries. The energy values for the first two triplet states 3Bu and 3Ag, obtained from TDDFT calculations, were found to be highly strongly correlated with the experimental values. Also, the theoretical calculations for the electronic transition 1 1Ag --> 1 1Bu were also extremely well correlated with their experimental counterparts; even more important, the three reported experimental data for 1 1Ag --> 2 1Ag transitions in these systems conformed to the correlation for the TDDFT 1 1Ag --> 1 1Bu transition. The first excited electronic state in the linear polyenes studied (from ethene to the compound consisting of 40 ethene units, P40) was found to be 1Bu. The energy gap between the excited states 2 1Ag and 1 1Bu decreased with increasing length of the polyene chain, but not to the extent required to cause inversion, at least up to P40. In the all-trans linear polyenes studied, the widely analyzed energy gap from the ground electronic state to the first excited singlet state for infinitely long chains may be meaningless as, even in P40, it is uncertain whether the ground electronic state continues to be a singlet.

Journal Article↗
PubMed2003

H-bonded N-heterocyclic base-pair phototautomerizational potential barrier and mechanism: The 7-azaindole dimer.

A theoretical analysis of the double proton transfer (PT) in a hydrogen-bonded N-heterocyclic base pair is presented. The calculated (time-dependent density functional theory) double PT barrier calculated for the concerted process of the 7-azaindole C(2h) dimer in the first excited singlet electronic state S(1) conforms well to the kinetic data and the photophysical evidence reported in this article. The calculated PT energy barrier of 4.8 kcal/mol height, and the corresponding zero point energy value, yield for the S(1) state an activation energy barrier of 0.3 kcal/mol. This finding implies that the double PT concerted process is almost barrierless, confirming previous experiments. Upon N-H deuteration of the 7-azaindole dimer, the theoretical excited-state activation energy for the double deuterium transfer is determined to be 1.4 kcal/mol, in agreement with experiment, which in low-temperature spectroscopy is shown to negate excited-state double-deuteron transfer.

Journal Article↗
PubMed2001

Spectrothermodynamic relationship of cationic vs anionic species derived from protonation vs deprotonation of pyrrolo-aza-aromatic bases in homologous series.

Theoretical research on the spectroscopy and protonation energies of ionic species related to the neutral pyrrolo-aza-aromatic bases has been carried out, using Density Functional Theory (DFT) and its time dependent form (TDDFT). In the ionic species the skeleton localized (+) and (-) charge in the protonated and deprotonated species is shown to have a strong perturbation of the pi-electronic states. The lowest electronic S(0) --> S(1) (pi,pi*) transitions are shown to have near-coincidence for each cation and anion for the whole homologous series, in agreement with the Valle-Kasha-Catalán rule previously stated. It is further demonstrated that simultaneous dramatic changes, upon electronic excitation, in acidity and basicity at the pyrrolo- and aza-positions of the molecular skeleton are the driving force for the biprotonic phototransfer processes in these bases. This constitutes confirmation of the proton-transfer rather than H-atom transfer as the reaction mechanism.

Anions↗
PubMed2001

Characterization of binary solvent mixtures of DMSO with water and other cosolvents.

Binary mixtures of DMSO with nine different cosolvents were characterized in light of the pure solvent scales, using suitable probe/homomorph couples. Various physical (vapor pressure, surface tension, viscosity, and enthalpy of mixing) and spectroscopic (IR and NMR) properties of the DMSO/water mixtures are described in terms of their polarity, acidity, and basicity, and the descriptions are examined with a view to establishing their potential physical significance.

Chemical Phenomena↗
PubMed2001

[Incidence of the cleft lip and palate in the University of Chile Maternity Hospital and in maternity Chilean participating in the Latin American Collaborative Study of Congenital Malformations (ECLAMC)].

BACKGROUND: ECLAMC is a registry, aimed to assess the incidence of congenital malformations, that started in 1967 and Chile incorporated to it in 1969. AIM: To report the incidence of cleft lip/palate, updated to 1999 in the University of Chile Maternity Hospital and other Chilean hospitals participating in the ECLAMC. PATIENTS AND METHODS: A review of the ECLAMC database that registers all births or stillbirths of more than 500 g. RESULTS: The incidence of orofacial cleft, at the University of Chile Maternity Hospital, in the period 1991-1999 was 17.8 per 10,000 (12.6 for cleft lip and 5.2 for cleft palate). The incidence in the rest of participating hospitals was 12.04 and 4.6 respectively. Males had a higher incidence of cleft lip and 80% of children with cleft palate, had other malformations, most of them as part of a syndrome (13 and 18 trisomy, holoproscencephalia, Pierre Robin, Apert en EE syndromes, anencephaly etc). In three of 12 children with cleft lip but without cleft palate, there was a relative with the same malformation. CONCLUSIONS: It is proposed that both entities, cleft lip with or without cleft palate and cleft palate without cleft lip, are two etiopathogenically different conditions.

Chi-Square Distribution↗
PubMed2000

Effects of medium on decarboxylation kinetics: 3-carboxybenzisoxazoles and their potential use as environmental probes in biochemistry.

The decarboxylation rate of the tetramethylguanidinium salt of 3-carboxy-6-nitrobenzisoxazole in 24 pure solvents and 36 dimethyl sulfoxide binary mixtures with diglyme, acetonitrile, benzene, dichloromethane, chloroform, and methanol was analyzed in the light of the SPP, SA, and SB pure solvent scales. The results allow one to rationalize the high sensitivity of this kinetics to the reaction medium and to assess the potential use of this compound as a probe in biochemical environments. The natural environment for comparison of this kinetics was found to be the gas phase rather than the aqueous medium. In the latter, the process is much faster owing to such high polarity, which, however, is strongly diminished by the high acidity of the medium. Based on our calculations, the rate constant for the decarboxylation kinetics in the gas phase must be in the region of 2 x 10(-10) s(-1) (i.e., 3 orders of magnitude smaller than in water).

Decarboxylation↗
PubMed2000

The role of personality, coping style and social support in health-related quality of life in HIV infection.

OBJECTIVE: To determine the role of health status, personality and coping style, on self-report health-related quality of life (QoL). METHODS: Participants were HIV seropositive individuals at all disease stages from three samples (a) gay/bisexual men from the UK, (b) injecting drug users from the UK, (c) injecting drug users from Italy. All participants completed questionnaires evaluating QoL, personality, coping style and social support. Explicit models of the relationships between the measured variables based on a review of the literature were tested using structural equation modelling. RESULTS: Health status was modestly associated with the physical but not the psychological aspects of QoL (beta = 0.44). Neuroticism was strongly associated with psychological QoL (beta = -0.73) but only weakly with physical QoL (beta = -0.21). The samples did not differ in either the pattern or the magnitude of these relationships. Mediating factors such as coping style, social support and other personality variables had only a weak influence on the role of Neuroticism. CONCLUSIONS: Neuroticism had a strong influence on health-related QoL that was independent of health status. Neuroticism was more strongly associated with the psychological aspects of QoL than health status. Coping styles and the other psychological variables assessed had only a weak mediating influence on this relationship.

Adaptation, Psychological↗
PubMed2000

The X chromosome frequently lags behind in female lymphocyte anaphase.

Pancentromeric FISH and X-chromosome painting were used to characterize anaphase aberrations in 2,048 cultured lymphocytes from a healthy 62-year-old woman. Of 163 aberrant anaphases, 66.9% contained either chromosomes or their fragments that lagged behind. Characterization of 200 laggards showed that 49% were autosomes, 33. 5% were autosomal fragments, and 17.5% were X chromosomes. The X chromosome represented one-fourth of all lagging chromosomes and was involved much more often than would be expected by chance (1/23). Labeling of the late-replicating inactive X chromosome with 5-bromo-2'-deoxyuridine revealed that both X homologues contributed equally to the laggards. Among 200 micronuclei examined from interphase cells, the proportion of the X chromosome (31%) and autosomal fragments (50%) was higher than among anaphase laggards, whereas autosomes were involved less often (19%). These findings may reflect either selection or the fact that lagging autosomes, which were more proximal to the poles than were lagging X chromosomes, were more frequently included within the main nucleus. Our results suggest that the well-known high micronucleation and loss of the X chromosome in women's lymphocytes is the result of frequent distal lagging behind in anaphase and effective micronucleation of this chromosome. This lagging appears to affect the inactive and active X chromosomes equally.

Anaphase↗
PubMed2000

Segregation of sex chromosomes in human lymphocytes.

Centromeric FISH was used to investigate the segregation of sex chromosomes in human lymphocytes. The aim of the study was to evaluate the effects of cell culture, cytokinesis block, age and sex on segregation and to compare the behaviour of the X and Y chromosomes. In uncultured T lymphocytes of five elderly women, the mean frequencies of nuclei hyperdiploid and hypodiploid for the X chromosome were not significantly affected by culturing the cells or by cytokinesis block. In cultured binucleate lymphocytes of two age groups of men, the X chromosome showed significantly higher mean frequencies of hyperdiploidy, hypodiploidy and reciprocal gain and loss than the Y chromosome. Reciprocal gain and loss of the Y chromosome was statistically significantly higher in the older than the younger men. In four women, studied in the same series, the rates of X chromosome aneuploidy did not significantly differ from those obtained in men. In conclusion, malsegregation of the X chromosome is common in lymphocytes of both men and women and more frequent than Y chromosome malsegregation. However, there is no clear sex difference for X chromosome reciprocal gain and loss. This would suggest that the high loss of the X chromosome in women, documented in metaphase studies, is due to micronucleation.

Adult↗
PubMed2000

The relationship of psychological variables and disease progression among long-term HIV-infected men.

This study investigated the contribution of psychological factors to disease progression among long-term HIV-1 infected gay men. Participants completed self-report measures including coping strategies, life events, social support, personality and psychological morbidity and were followed clinically for up to 30 months. Cox proportional hazards survival analyses were carried out to CD4<200 x 106/1 and AIDS-related complex (ARC) or AIDS diagnosis controlling for viral load, antiretroviral drug use and CD4 count. Only acceptance coping was a significant predictor of time to ARC or AIDS diagnosis: the risk of ARC or AIDS was almost 5 times greater for those scoring within the lowest tertile compared with those scoring in the highest tertile (HR=4.7, 95% CI 1.8-12.3).

AIDS-Related Complex↗
PubMed2000

Drug treatment of HIV associated neuropsychiatric syndromes.

Psychotropic drugs are frequently used to treat the wide range of neuropsychiatric syndromes that patients infected with the human immunodeficiency virus (HIV) may develop. In order to administer these agents properly, physicians should take into account, among other factors, that: the central nervous system (CNS) of these patients is often impaired; they tend to suffer from one or more physical disorders; and they may be taking various other medications. The present paper reviews the clinical features and the general guidelines for administering neuroleptics, antidepressants, psychostimulants, benzodiazepines, opiates, lithium and carbamazepine in this group of patients, based on the literature and the authors' own clinical experience.

HIV Seropositivity↗
PubMed1999

Resolution of concerted versus sequential mechanisms in photo-induced double-proton transfer reaction in 7-azaindole H-bonded dimer.

The experimental and theoretical bases for a synchronous or concerted double-proton transfer in centro-symmetric H-bonded electronically excited molecular dimers are presented. The prototype model is the 7-azaindole dimer. New research offers confirmation of a concerted mechanism for excited-state biprotonic transfer. Recent femtosecond photoionization and coulombic explosion techniques have given rise to time-of-flight MS observations suggesting sequential two-step biprotonic transfer for the same dimer. We interpret the overall species observed in the time-of-flight experiments as explicable without conflict with the concerted mechanism of proton transfer.

Journal Article↗
PubMed1999

The burden of care: the impact of HIV-associated dementia on caregivers.

It has been suggested that up to 15% of patients with AIDS may develop HIV-associated dementia. The syndrome may be either abrupt or insidious and is characterized by poor prognosis. Increasing cognitive impairment will necessitate the patient receiving a substantial amount of care and support in the community in addition to medical treatment and periods of hospitalization. The impact of caregiver burden is reasonably well documented in Alzheimer's disease, but there is a dearth of literature relating to caregiving and HIV-associated dementia. The current investigation is an observational study based on a small group of individuals which evaluates the experiences of these particular individuals as they care for their partner, friend, or son with HIV-associated dementia. The caregivers experience the stresses described in the non-HIV dementia literature; however, the nature of HIV disease means that there are issues involved in caring for this patient group that distinguish it from other types of dementia care; these include difficulties relating to specific HIV medical problems and problems with service shortfalls. The caregiver is more likely to be a parent or partner than a child of the patient due to the early age onset seen in this disease compared with Alzheimer's disease. Caregivers express their need for information about dealing with the everyday physical, behavioral, and emotional challenges and about services and benefits available. The interviewees expressed concerns over a perceived lack of communication and information from professionals involved in the patient's care and in the provision of services. The study offers an insight into the relevant issues affecting such caregivers and suggests areas of unmet needs that might be addressed in future service provisions.

AIDS Dementia Complex↗